INVENTION OF CHRONOMETERS, &C, ^QJ 



only prove that he intended to make experiments on the wide 

 and narrow vibrations of the balance; and falls short of 

 the hints contained in Dr. Hooke's Postscript, which we have 

 already quoted. But though we cannot allow Berthoud the 

 credit of originality, it is impossible to deny that his researches But the re- 

 possess an eminent share of merit ; and we have no doubt but f^^''<^hes and 

 * ' labours of 



that their publication has been of great service to artists, in Eerthoud are 



that essential part of the construction of timekeepers, gei-. of great value, 



* ^ and import- 



thoud found that the spiral spring, in order to be isochronal, ance. 

 must have an ascending force in arithmetical progression, and ^^ discovered 

 that this property may be effected, not only by the length of the force of an 

 spring, but by the number of coils, and the tapering or de- ^^°^- *°"^ 

 creasing thickness from the centre to the extremity, &;c. He and the 

 adds besides the proportions of the tapering in many springs, affecrt^ 

 which he had actually tried, and gives minute accounts of the 

 experiments made with them in several timekeepers. 



The late Mr. Arnold applied to the balance the cylindrical Aroold applied 

 or helical spring, which had been employed long before to a or\eHcal ^ 

 variety of purposes instead of the spiral, which had been con- spring to chro- 

 stantly used in watches since the time of Dr. Hooke and M. "elSng^its ^''^' 

 Huygens.* This is one of the articles of his patent of 1782, superiority to 

 and the specification is contained in these words: '^ Tke in- ^pira j. 

 *' curvating of the ends of the helical spring is attended xiith 

 " the property of rendering all the vibrations of equal duration^ 

 " because the fgure is always similar to itself" Whence it He affirms 

 would appear, that provided the spring be made of that form, c^ronar lf*the 

 the vibrations cannot fail to be isochronal ; but experience is fi^ed end 

 contrary to that notion, and artists are obliged to attend to a ^'^v'ards^- ^ 

 variety of circumstances in the application of the helical, as —but this is 

 well as that of the spiral spring. Mr. Arnold was asked by "^^ ^ ^ ^'^'* 

 the Committee of the Housgi of Commons, to which the petition 

 of Mr. JMudge was referred, f " What objections are there 

 " against the common spiral spring?" To which he answered, 

 *• That it is never a spiral, but when it is at rest ; for the 



* One of Harrison's watches had an helical spring. See EarO'- 

 shaw's Disclosure; who says the machine is now at Greenwich. 



W.N. 



f Report fromthe Select Committee, &c. ordered to be printed, 

 11th June, 1793. p. 81. 



Vol. XIV. — August, 1806. Qq ^'instant 



